Transferring power from a rotating engine or motor to a transmission or other implement requires an attachment mechanism to absorb the rotational torque differential between the engine and the desired transmission or implement. The attachment maintains a specific relationship of the components to prevent unwanted loss of energy from friction associated with misalignment of the rotating shaft from the motor with a transmission or other component. Additional consideration is given for the forces generated from the environment the assembly is to be employed. In an internal combustion engine the area between the engine and the transmission is commonly called a bellhousing. Historically Automobile, Truck, and Implement Manufacturers have provided their bellhousings from several processes; namely metal casting; metal pressing using dies and presses and occasionally a hydro form pressing method requiring a less costly form of die.
A bellhousing also provides an area for controlling power transfer from the motor to the attachment to it.
Inside the bellhousing a clutching mechanism and often a starting system for the motor is placed. The bellhousing encapsulates these mechanisms protecting the components from the outside environment and hopefully contains any failure of the components within the bellhousing.
Bellhousings are attached to the motor with taps and commonly to the transmission or implement with taps. The pattern of the tapped holes varies from manufacturer to manufacture and from motor type to motor type as well as transmission type to transmission type. Additional variations occur within subgroups from above to accommodate the clutching and starting systems required for each application. Manufacturers most often design and build a casting from aluminum or iron for each application. The process requires a large commitment of capital and time designing the molds. They can only justify the large initial startup costs through the economics of mass production.
The manufacturer is faced with a tradeoff of weight versus strength when selecting either aluminum or steel. In the marketplace there has developed a need for a lighter weight steel bellhousing to accommodate the manufacturer's production needs. New high torque engines create stresses that cause failure of the traditional cast bellhousing.
In areas of motor sports all the circumstances above; flexibility of application; strength versus weight; production cost; and safety are equally important. Most motor-sport sanctioning bodies are now requiring bellhousings capable of containing all the components within the bellhousing in the event of a failure. Most require a steel bellhousing. Modern engines are producing torque in excess of the design parameters of traditional bellhousing. The consumer desires an affordable and safe bellhousing that can be tailored to multiple combinations common in their competition. This market is not economically viable for traditional mass production methods since the price per piece is not sufficiently off set by production numbers.
Automotive restoration and modification has demands similar to the motor sport consumer. The flexibility and strength of the spun bellhousing enables combinations of almost any imaginable at a reasonable cost. Likewise, all high torque, limited production applications of rotating energy from a motor to an attachment will benefit from the lower per unit cost of spun bellhousing.